In recent years, in analysis or treatment of a polymer compound such as nucleic acid, protein, and sugar chain, magnetic bodies of a micro particle diameter including extremely minute nano-sized magnetic bodies have been used in order to further increase the solid phase surface area to thereby achieve a higher level of reactivity. Moreover, even with micro-sized living organisms such as cells and bacteria, with magnetic bodies of a micro particle diameter having a certain type of receptor being efficiently bonded to the surface of the biological body, the biological bodies can be covered. By mixing and suspending magnetic bodies of a micro particle diameter with and in a solution containing a target polymer compound or a target living organism in this manner, a treatment such as detection, separation, isolation, and extraction of the target polymer or the target living organism can be performed more efficiently, compared to a treatment that uses magnetic particles of a common micro size (1 to several 100 μm).
If an automated system is available as being provided with a magnet that recovers magnetic bodies by easily and quickly recovering this type of magnetic bodies of a micro particle diameter using an external magnetic field without any need for steps of centrifugal separation and filtration, it will provide a great advantage in a wide range of fields such as isolation and production of DNA and mRNA in the area of genomic research, isolation and production of protein and peptide, and protein-protein interaction analysis in the area of proteomics research, and pharmacologic targeting and pathogenic virus detection in the area of medicine. In particular, an advantage is anticipated in sectors including nucleic acid extraction, peptide extraction, and immunoassay.
However, if the particle diameter of magnetic bodies becomes minute, the magnetic moment possessed thereby and the magnetic flux passing therethrough become smaller. Consequently, there is a problem in that separation and capturing of magnetic bodies requires a larger amount of time, prolonging the amount of time required for a treatment, and it may become difficult to perform a complete separation treatment in a short period of time. For example, in a case where a magnetic field is applied to the interior of a dispensing tip and magnetic bodies are separated by adsorbing them on the inner wall thereof while being suctioned or discharged, since the size of the magnetic flux passing through the magnetic bodies is small, the speed of suction/discharging needs to be lowered and the treatment may require a larger amount of time. Moreover, when suctioning a reagent solution or the like, there is a possibility that magnetic bodies of a micro particle diameter, which should have been adsorbed, may flow out from the dispensing tip. Meanwhile, there is a problem in that when an attempt to adsorb magnetic bodies is made with application of a magnetic field using a powerful magnet, they become agglutinated in a pellet shape more strongly as the particle diameter thereof becomes more minute, and consequently the amount of time required for re-suspension may further increase.
In order to improve these points, there has been practiced a method such that as a polymer composition that becomes responsive depending on temperature, there is used temperature responsive magnetic particles in which a polymer that shows the upper critical solution temperature in a state of being an aqueous solution is fixed on magnetic particles of a particle diameter of 100 nm to 200 nm (Patent Document 1). In this method, the aqueous solution of the temperature responsive magnetic particles is heated, keeping the temperature at not more than the upper critical solution temperature, and the temperature responsive magnetic particles are agglutinated. Then, a magnetic field is applied thereto, and recovery thereof is performed. In this case, for separation of the particles, temperature control needs to be performed with use of a temperature control device, and consequently there is a problem in that the device may become complex and operations may become troublesome, resulting in an increase in the amount of time required for a treatment.
On the other hand, there has been a micro column system in which a porous member manufactured with sintered iron beads is fixed within a column, and by applying a magnetic field to the porous member when a solution containing micro magnetic particles is passing therethrough, these micro magnetic particles are separated (Patent Document 2). In this case, the solution that contains the magnetic particles is flowed unilaterally in the discharging direction of the column, to thereby capture and separate the magnetic particles. Accordingly, in order to completely capture the magnetic particles contained in the solution, it is necessary to dilute the solution or increase the amount of the reagent to thereby increase the amount of the liquid, and to circulate it while pressure is being applied. As a result, there is a problem in that the device may become complex, resulting an increase in the amount of time required for a treatment or in an increase in the amount of the reagent. Furthermore, since the magnetic particles are captured by adsorbing them in several pores of the sintered body fixed within the column, there is a problem in that it may become difficult to perform a treatment in a short period of time in which the sintered body is cleaned by making a cleaning liquid flow thereon, and the magnetic particles that have been re-suspended and further re-suspended in the liquid are concentrated. Moreover, there is a problem in that the porous member is fixed in the column, and it may have a lower chance of encountering magnetic carriers within the liquid, compared to the same amount of particle-shaped members, which are capable of freely moving within the entire liquid.